Energy consumed by humankind is limitative and global warming caused by carbon dioxide generated by using the energy is the greatest problem of humankind with an energy crisis. Accordingly, energy regulations of each country become tightened and an energy rating system with respect to home appliances is a permanent problem that manufacturers have. An energy rating system of the government which requires maximum efficiency using less energy well accords with needs of consumers who desire high internal capacity and low power consumption. Particularly, many studies with respect to refrigerators have been performed for past several ten years, and studies for efficiency improvement of a cooling cycle, a compressor, a heat exchanger and the like have reached the limit. Accordingly, recently studies with respect to thermal losses are mainly performed and many attempts to increase energy efficiency by strengthening heat insulation performance of refrigerators have been performed.
An insulation material such as existing polyurethane has about 20 mk/m·K. When the insulation material is used, a thickness of an outer wall of a refrigerator becomes greater in such a way that storage capacity of the refrigerator becomes reduced.
Accordingly, to solve these problems, it is necessary to use a vacuum insulation panel having excellent heat insulation performance.
To further improve heat insulation performance of a vacuum insulation panel, it is necessary to form a high vacuum in the vacuum insulation panel and then to maintain the high vacuum. When a vacuum pumping process in a vacuum chamber is performed to manufacture a vacuum insulation panel in a high vacuum, a long time may be consumed for forming a high vacuum in the vacuum insulation panel. Also, depending on types of core material, since a core material may be discharged as particles outside the vacuum insulation panel during the vacuum pumping process, an additional process may be required. Also, when a vacuum insulation panel is manufactured by vacuum-pumping in a vacuum chamber, since not only manufacturing costs thereof are high but also it is impossible to artificially control a shape of the vacuum insulation panel from the outside after the vacuum insulation panel is disposed in the vacuum chamber, it is difficult to manufacture a three-dimensional shaped vacuum insulation panel. Also, even when a vacuum insulation panel in a high vacuum is manufactured, it is difficult to maintain the high vacuum.